The use of a detachable "process cartridge" on an image forming apparatus such as an electrophotographic (EP) printer is fairly old, having been introduced by Canon in U.S. Pat. No. 4,500,195. This process cartridge included the major components of an EP printer that, during use, become worn or are consumed, such as toner material in a reservoir, a developer unit, a cleaner unit, and a photoconductive (PC) drum.
Another Canon patent, U.S. Pat. No. 4,551,000, discloses a removable "process kit" for an image forming apparatus, in which this process kit contains "consumable members," such as a photoconductive drum, developer unit, cleaner unit, and toner reservoir. The process kit also includes an apparatus "for indicating when the useful life of the process kit is about to expire and when it has expired," which comprises an electronic counter circuit that includes a memory to store the number of operations of the PC drum. The process kit can also contain an LED to act as a warning indicator that the service life has expired, or is about to expire. The counter/memory circuit is provided as part of the process kit. An electrical power source is provided to the counter circuit at all times, whether or not the process kit is attached to the main body of the printer or copier. In this manner, the content of the counter is not erased, but is kept in memory.
The above Canon '000 patent is probably the first patent disclosure to provide a non-volatile memory circuit on a replaceable process cartridge used with a printer or copier. Many other patents or other publications have since added to the list of technical disclosures providing a memory circuit on a replaceable process cartridge, typically to store some type of information, usually in a non-volatile memory device. For example, a method of storing (in a counter variable in a memory device on a process cartridge) the number of prints or copies that have been made is disclosed not only in Canon '000, but also in Japanese patent disclosure document JP 05210304(A), owned by Fujitsu. In JP 05210304(A), the types of information being stored include values of a sheet counter before and after use of the cartridge, number of rotations and time for rotation of a developing roll, and number of rotations and time for rotation of a photosensitive drum.
Another type of information stored in a conventional process cartridge memory device is a cartridge identification number that can be detected by the printer/copier main body when the cartridge is attached. U.S. Pat. No. 5,132,729 (owned by Minolta) discloses an image-forming apparatus having a removable and replaceable having a memory device that stores a recognition number (i.e. a "unit number") of the image-forming unit, and a separate memory unit on board the printer that contains ROM and RAM to test whether or not the unit number is proper with respect to a manufacturer's code. If the process unit is not authentic, the printer or copier can be disabled. Moreover, JP 08069213(A) (owned by Canon) not only stores the serial number, but also stores a counter value, and two different processing conditions. Copying is inhibited if the most significant byte of the serial number is not equal to zero (0) and if the unused areas of addresses 5-63 are not FF (in hexadecimal).
A concept found in some conventional printer/copiers is the ability to limit the service life of a process cartridge based on information being stored in the process cartridge. An example of this is U.S. Pat. No. 5,276,461 (owned by Tokyo Electric) which discloses a laser printer having a replaceable photosensitive cartridge and also having a non-volatile memory mounted to a card base plate. The non-volatile memory comprises an EEPROM integrated circuit, which has a new count value incremented every time the printer produces a new printed sheet of print media. When the photosensitive drum nearly reaches the end of its service life (with regard to the number of copies it has produced), then a message is placed on a display of the printer (and also can be sent to a host computer) to indicate the photosensitive drum must be replaced soon. When the photosensitive drum reaches its maximum number of copies, a new message is displayed saying that the drum has expired, and, in addition, a solenoid ejects the card base plate from its plug-in socket in the microprocessor of the printer, thereby disabling the printer. JP 63212956(A) (owned by Bando Chemical) also determines the remaining service life of a cartridge, primarily based on the remaining quantity of toner, and stores that information in a memory device provided on the cartridge. The remaining quantity of toner or the remaining service life of the photosensitive body are used to calculate the remaining service life of the cartridge, and this information is stored in the memory.
Another concept found in some conventional printer/copiers is the ability to store operating parameters information and to adjust the copier's operating conditions accordingly. This concept is disclosed in U.S. Pat. No. 5,272,503, and also in JP 58132758(A) and JP 08069212(A). U.S. Pat. No. 5,272,503 (owned by Xerox) discloses a printer having an operator replaceable cassette that includes a non-volatile memory device (i.e. an EEPROM). The EEPROM stores a value that varies as a function of the usage of the replaceable cassette. For example, the EEPROM can store the number of prints that have been made using that cassette. This information is later used to adjust certain operating parameters of the printer, including the photoreceptor charge level, exposure level, developer bias level, and the response level of the automatic density control system. The printer also contains a non-volatile memory which is updated by the accumulated print count that is stored in the cassette EEPROM. If the printer determines that an update is due, a new value is written into the cassette's EEPROM memory, where it is retained even if the cassette is later removed from the printer.
JP 58132758(A) (owned by Canon) discloses a process kit used in an image formation device in which a PROM is built on the process unit. Certain information is stored in the PROM, including information to determine exposure, quantity of electrostatic charging, developing bias value, and destaticizing exposure. JP 08069212(A) (owned by Canon) discloses an image forming device that has an exchangeable drum unit, which incorporates a non-volatile memory device. The memory device stores a serial number, counter value, and processing conditions. The processing conditions represent a correction value for the dispersion of the sensitivity of the drum.
Some of the conventional printers/copiers use process cartridges that can have more than one load of toner run through their developer. For example, U.S. Pat. No. 5,548,374 (owned by Toshiba) discloses a printer with two counters which count the total rotations of the photoconductive drum and the total number of toner additions. In one embodiment, the counters are mounted on the printer; in a second embodiment, the counters are mounted in the process unit that contains the toner hopper. A further example is JP 06067484(A) (owned by Ricoh), which discloses an image forming device having a toner supply cartridge that is detachable from a developer unit. The developer unit is provided with an EEPROM, which stores the number of times that toner cartridge attachment is carried out. When the number of times cartridge attachment occurs reaches a reference value, the output of the image forming device is inhibited to prevent an inferior image from being made due to the end of the service life of the developer unit.
Some of the conventional printers/copiers provide process cartridges having memory devices that blow fuses or set memory locations in one direction only (i.e., a "one-way memory" device). For example, U.S. Pat. No. 5,021,828 (owned by Fuji Xerox) discloses a copy machine that includes a "process kit" that has a mechanical counter to count the number of rotations of the photosensitive drum. The process kit also contains at least two fuses, which are blown after a certain number of copies have been made. In the illustrated embodiment, two fuses are included on the process kit, and the first one is blown after 99 sheets have been copied, and the second fuse is blown after 16,000 sheets have been copied. After the second fuse is blown, the consumable items (i.e., toner, etc.) have been expended, and the process kit has come to the end of its life; however, the copier will allow another given number of copies to be made as "grace" copies after the second fuse has blown. The fuses can comprise semiconductors, including diodes or transistors.
Another example of a "one-way memory" device in disclosed in U.S. Pat. No. 5,491,540 (owned by Hewlett-Packard), in which a printer/copier changes a memory location in a memory chip after a certain amount of use. The printer/copier can receive replacement parts, such as a developer cartridge. A memory chip is mounted to the cartridge and is connected to a control computer on the printer side via a single electrical wire. The memory chip can store serial number information for the replacement part, and can also store operational data such as the amount of previous use of the replacement part and how its physical characteristics may have changed over use. The single wire configuration is used so that this new cartridge can replace existing replacement cartridges that use a fuse that can be blown after a certain amount of use.
A further example of a "one-way memory" device in disclosed in U.S. Pat. No. 5,283,613 (owned by Xerox), in which an electrophotographic printer/copier irreversibly sets individual bits in a "flag memory" after a certain multiple of prints have been made by a copy machine. Replaceable cartridges are provided with the copy machine, and the cartridges include a non-volatile memory that is divided into two sections: an electronic "count" memory and an electronic "flag" memory. The count memory maintains a one-by-one count of prints made using the cartridge, while the flag memory sets individual bits upon a certain multiple of prints being made. The count memory can be both read from and written to, however, the flag memory can have its bits alterable from a first state to a second state, but not alterable from the second state back to the first state. The flag memory can be inspected as a tamper-proof check of the actual count value of the pages that have been printed. Once one of the flag bits is set, this lowers the limit of possible allowable remaining count values in the count memory, which in the preferred embodiment uses a counter that counts down from 20,000 to zero copies that are yet available from this cartridge. The type of memory device is disclosed as being a PROM, or an EEPROM which has its charge pump disabled or omitted. Because of this hardware structure, each flag bit can be altered only "downward." The flag bits are set strictly upon a multiple of the prints that have been produced, not upon toner depletion or any other parameter.
Yet another example of a "one-way memory" device in disclosed in U.S. Pat. No. 5,365,312 (owned by Mannesmann AG) which uses a "telephone card" as a memory that can have its contents erased on a bit-by-bit basis. The memory is located on a reservoir, and the memory stores information about the current fill status of the reservoir and the expiration date of the printing medium, relevant for this particular printer. The inventor prefers that the memory on the reservoir be non-volatile, and this memory can be in the form of an integrated circuit, or as a "telephone card" in which a memory strip is contained on the telephone card and can have its contents erased bit-by-bit. In one example, a single memory strip bit is erased for each 10,000 ink droplets printed. Once one of these bit is erased, the bit's modification is irreversible. A timer can also be included that will contain information about the expiration date of the ink fluid. Another read-only memory can be used to store an ID code to identify the ink reservoir. Finally, the counter can be used to activate an alarm when the count value reaches a minimum supply level of the toner.
The conventional image forming printers and copiers could be improved by measuring the actual quantity of remaining toner material in their toner reservoir to enable the image forming apparatus to make more intelligent decisions as to how the apparatus should function with a particular process cartridge. Another improvement would be to store machine operating data in an image forming apparatus, including in a non-volatile memory device mounting on the process cartridge, including data that is stored in an irreversible manner. A further improvement would be to provide alternative means to disable or enable certain functions in an image forming apparatus, including functions that are unrelated to one another.